1. Field of the Invention
The present invention generally relates to the field of breath alcohol detection systems. In particular, to fuel cell breath alcohol detection systems that have the ability to detect the presence of mouth alcohol.
2. Description of Related Art
An alcoholic beverage is a drink containing ethanol, commonly known as alcohol, although in chemistry the definition of alcohol includes many other compounds Alcohol, specifically ethanol, is a psychoactive drug and is a powerful central nervous system depressant with a range of side effects.
Alcohol has a biphasic effect on the body, which is to say that its effects change over time. In the initial stages of intoxication, alcohol generally produces feelings of relaxation and cheerfulness. Further consumption however affects the brain leading to slurred speech, blurred vision, clumsiness and delayed reflexes, among other coordination problems. This condition is commonly referred to as intoxication or drunkenness, and eventually subsides when the alcohol has fully metabolized in the body.
When a human drinks alcohol, the alcohol housed in the stomach passes into the bloodstream. Cell membranes are highly permeable to alcohol, so once alcohol is in the bloodstream it can diffuse into nearly every biological tissue of the body. Once in the bloodstream, the alcohol circulates to the brain, resulting in intoxication, loss of inhibition and impairment of motor skills such as driving a vehicle. The amount of alcohol consumed and the circumstances surrounding consumption play a large role in determining the extent of an individual's intoxication. Examples of such circumstances include the amount of food in the stomach at the time of alcohol consumption and the hydration level of the individual at the time of consumption, among others.
Due to the coordination impairment and other symptoms associated with intoxication and drunkenness, most countries have laws against drunk driving, i.e., driving with a certain concentration of ethanol in the blood. The legal threshold of blood alcohol content ranges from 0.0% to 0.08%, depending on the jurisdiction. Punishments for operating a vehicle over the legal limit in a given jurisdiction generally include fines, temporary loss of an individual's driving license and imprisonment. Creation of these laws has led to a market for devices to accurately measure the blood alcohol content of individuals operating motor vehicles.
Blood alcohol content (BAC) or blood alcohol concentration is the concentration of alcohol in the blood (weight per unit volume). While blood alcohol content can be directly measured in a hospital laboratory setting, it is more common for it to be measured in law enforcement situations by estimation from an individual's breath alcohol concentration using a breath alcohol testing machine.
Breath Alcohol Concentration (BrAC) is commonly measured in grams of alcohol per 210 Liters of breath (g/210 L) or milligrams of alcohol per Liter of breath (mg/L). However, there are other units of measure as well used by those skilled in the art.
Breath alcohol testers assume that the individual being tested is average in various ways. For example, on average the ratio of BAC to breath alcohol content (the partition ratio) is 2100 to 1. In other words, there are 2100 parts of alcohol in the blood for every part in the breath in an equal volume. The actual ratio can vary from person to person and moment to moment. However, it is generally accepted that a partition ration of 2100:1 underestimates the actual blood alcohol concentration of individuals, i.e., is in favor of the subject in a legal sense.
For purposes of law enforcement, most jurisdictions don't concern themselves with the exact amount of impairment due to drinking. Rather, they follow the so-called “per se” laws by which an individual's measured BAC or BrAC level is the primary method used to define intoxication and provides a rough measure of an individual's impairment. Although the degree of impairment varies among individuals with the same BAC, since BAC or BrAC are objective measurements they are therefore legally useful and difficult to contest in court.
In the field of breath alcohol testing, it is well known that if a breath measuring instrument analyzes an alveolar (deep lung) sample of breath, the concentration of alcohol in that sample is a reliable indicator of a human subject's intoxication level. This is because the alveolar breath is in equilibrium with the blood due to the intimate communication between blood and breath in the lung, between capillaries and alveoli.
Generally, when an alcohol breath test is made, the subject is required to blow into a measuring instrument. Instruments use various sensors to determine when alveolar breath is delivered (as opposed to upper respiratory breath from the mouth or throat) so that an accurate measurement of deep lung air may be made, Those skilled in the art realize such methods might include measurements of flow, volume, time, pressure, or real-time breath alcohol concentration profiling.
Making a measurement before alveolar air has migrated from the lungs to the instrument during a blow will typically result in a low reading. This is because breath from the upper respiratory tract generally has a lower concentration of alcohol than deep lung air.
There is a condition where the breath generated from the upper respiratory tract has a higher concentration of alcohol than deep lung air. This is generally known as “mouth alcohol” and is typically the result of an alcoholic drink within the 15 minutes previous to the tested breath sample. This condition can cause a falsely high breath alcohol tester reading since the reading is not a pure sample of alveolar breath. By definition, mouth alcohol was not absorbed through the stomach and intestines and passed through the blood to the lungs. As stated previously, in analyzing a subject's breath sample, a breath alcohol tester is making an assumption that the alcohol in the breath sample came from alveolar air, i.e., air exhaled from deep within the lungs. However, alcohol from the mouth, throat or stomach may have contributed to the reading under certain conditions.
With virtually any current alcohol breath tester, one can easily prove the existence of mouth alcohol and its distorting effect on measured alcohol concentration. This is most easily observed when a subject is sober. Table 1 below provides data from an experiment meant to illustrate mouth alcohol's presence and effect. Subjects of such an experiment are not intoxicated. However, current fuel cell alcohol breath testers do not take into account the presence of mouth alcohol. In recognition of mouth alcohol's distorting effects on an alcohol breath tester's results, certified breath operators are trained to carefully observe a test subject for at least 15-20 minutes before administering the test to insure nothing is placed into the individual's mouth as a way to help guard against mouth alcohol contamination.
TABLE 1ResultTime (mm:ss)Action(g/210 L)Comment 0:00Blow0.000Sober Subject 0:30——Swish ½ ounce of vodka inthe mouth for 15 seconds. Spitvodka out; don't swallow. 1:50Blow0.352Maximum reading on many breathtesters is 0.400 g/210 L. This levelmay be lethal. 4:50Blow0.101In many U.S. states, this reading isover the legal driving limitof 0.080 g/210 L. 6:00Blow0.059In some European countries, thislevel will result in loss oflicense. 7:10Blow0.040In many workplaces, this readingand above would result intermination. 8:45Blow0.020In many workplaces, this readingand above would result indisciplinary action.10:00Blow0.011In some jurisdictions, juvenilesat this level will lose theirdriving license.11:15Blow0.008—12:30Blow0.006Many breath testers don't evenread this low.14:00Blow0.004—15:30Blow0.00015 minutes has expired sincealcohol was introduced into themouth.
To combat the problems of mouth alcohols, traditionally, in law enforcement, an officer will observe the subject for fifteen minutes prior to a breath test so that the officer may be able to testify in court that the subject did not put anything in the mouth, including alcohol, at anytime during the fifteen minutes prior to submitting a breath sample for measurement. In addition, the jurisdiction will typically require that two tests be taken on the subject separated by some number of minutes. The two tests must agree within a certain range or else the test is not valid. If the two tests agree, this gives further weight to evidence that no mouth alcohol is present.
However, since the problems of falsely higher tester readings due to mouth alcohol have become more widely known, manufacturers of breath alcohol test equipment have developed a variety of techniques to detect a mouth alcohol condition during a subject blow and report to the operator that a valid alcohol breath test is not possible at this time. Current known systems of mouth alcohol detection are all based on infrared absorption measurement systems and are known to those skilled in the art. These systems monitor the breath alcohol concentration of the blow from the beginning to end and look for distinctive profiles of breath alcohol concentration over time to determine whether there is a mouth alcohol condition. Those skilled in the art realize that these infrared detection systems might vary in their ability to detect all mouth alcohol conditions depending on the characteristics of the specific system used, those characteristics being as follows:
Signal-to-noise ratio.
Signal stability under varying ambient conditions.
Degradation of the measurement chamber components over time.
Deadspace of the system.
Specific detection algorithms.
Because of their added benefit of credibility, buyers of breath alcohol testers used in law enforcement often require mouth alcohol detection systems. These systems are most often used in conjunction with a 15 minute observation period to give further weight to evidence provided by the breath tester. Further, most jurisdictions require two consecutive breath tests on a subject. These two tests are typically spread over a small time period and must agree within a certain tolerance, such as 0.020 g/210 L. If the two tests do not agree, this may also be a sign of a mouth alcohol condition. Many buyers have also developed evaluation test regimens to determine the effectiveness of a given mouth alcohol detection system.
Some jurisdictions are now performing evidential breath tests on the roadside at the time of arrest. A test taken roadside is always closer to the subject's active drinking time than if the subject were driven to a station before testing. This makes mouth alcohol detection even more of a concern than in the past.
In summary, current alcohol testers in law enforcement have developed a three-legged approach to ensure that a breath test result is a true indication of a subject's BAC, showing no effects of a mouth alcohol condition:                1. A fifteen minute observation period of the subject before testing.        2. Two consecutive tests on a subject separated by a small time period that must agree within a certain tolerance.        3. Mouth alcohol detection by the breath-measuring instrument.        
A variety of techniques are currently available to detect a mouth alcohol condition during a subject blow and report to the operator that a valid alcohol breath test is not possible at that time. As stated previously, current known systems of mouth alcohol detection are based on infrared absorption measurement systems. Many infrared-based breath testers consist of a measuring chamber that a subject's breath passes through continuously during a blow. In its simplest form, a detector across the sample chamber from an infrared source can measure the amount of infrared energy absorbed by the alcohol molecules in the breath in between. The higher the concentration of alcohol, the more energy is absorbed. This forms the basis of an instrument that can measure and report accurate alveolar breath alcohol concentrations.
A principal advantage of infrared is that it is a real-time continuous measuring system that can profile the alcohol concentration of a subject blow from beginning to end. Algorithms can then analyze this profile of concentration versus time and notify the operator when there are indications of mouth alcohol.
An infrared breath profile of a drunken subject, without the subject having mouth alcohol, taken with current technology is exemplified in FIG. 1. At the beginning of the blow, as the lower concentration upper respiratory tract empties, the concentration begins to climb as deeper and deeper lung air begins to empty into the instrument. As the lungs approach the end of exhalation, the concentration reaches a plateau, indicating that deep lung alveolar breath is being measured. The plateau level is considered the measurement for that blow.
When a subject blows similarly, but with a mouth alcohol condition, the early concentration profile from the upper respiratory tract can actually be higher than the alveolar concentration. Without mouth alcohol detection algorithms, this could result in an incorrect reading on the subject, or the inability to make a reading at all. A typical such curve is indicated in FIG. 2 and could typically be detected by an infrared-based mouth alcohol detector.
Another current type of breath alcohol tester is the fuel cell breath tester. Typically, current fuel cell sensors do not perform a continuous real-time analysis of a breath exhalation like the infrared systems. Fuel cell systems typically use other means to determine when deep-lung air is present in the measuring chamber, by monitoring characteristics of the subject blow such as flow, volume, time, and pressure, along with certain algorithms known to those skilled in the art. When the system has determined that alveolar air is present, a small fixed volume of breath is taken into an electrochemical fuel cell. The alcohol is burned in the fuel cell and a certain number of electrons are produced for each molecule of alcohol burned. These electrons are counted by an external circuit and a measurement is produced. By always taking a fixed volume sample, the test is standardized; when the breath sample contains twice the concentration of alcohol compared to another sample, twice the electrons are produced and the measurement is twice as large.
A principal advantage of fuel cell systems over infrared systems is lower procurement and maintenance costs. Even with adding sensors for flow, volume, time, or pressure, the fuel cell based system can be made at much lower cost. The drawback of current fuel cell systems compared to infrared is the lack of a real-time, continuous measurement system; i.e. the instrument itself does not have the ability to detect mouth alcohol. To compensate, many fuel cell users still incorporate the two legs of a mouth alcohol system, i.e., a fifteen minute wait, and the two subject tests mentioned above. However, they lack the third leg, i.e., an instrument-based detection system.
Some systems have attempted to combine the advantages of both systems and include instruments that contain dual analysis systems, i.e., infrared and fuel cell. This is meant to offer a system that overcomes the disadvantages of each type, but becomes costly. Other dual technology has used a lower-cost infrared system just for mouth alcohol detection and used the fuel cell only for the measurement of final result. However, this system also suffers a cost disadvantage compared to a strictly fuel cell based system.